Physics 214 Midterm Fall 2003 Form A

Transcription

1 1. A ray of light is incident at the center of the flat circular surface of a hemispherical glass object as shown in the figure. The refracted ray A. emerges from the glass bent at an angle θ 2 with respect to its incident angle since the angle of incidence equals the angle of reflection. B. does not emerge from the glass due to total internal reflection. C. emerges from the glass parallel with the refracted ray because the beam is perpendicular to the glass-air surface where it emerges. D. is absorbed due to the difference in the indices of refraction between air and glass. E. none of the above. 2. In the figure, a real inverted image I of an object O is formed by a certain lens (not shown); the object-image separation is d = 38.0 cm, measured along the central axis of the lens. The image is just half the size of the object. What are the lens characteristics? A. Convex, focal length 38.0 cm B. Concave, focal length 38.0 cm C. Convex, focal length 8.4 cm D. Concave, focal length 8.4 cm E. No such lens exists Page 1

2 3. A large block of plastic is solid except for an air-filled void in the center of the block. The void is in the shape of a converging lens. A ray of light traveling parallel, but slightly above or below the central axis of the "lens" will: A. be bent toward the axis because the void acts like a diverging lens. B. be bent away from the axis because the void acts like a diverging lens. C. be bent toward the axis because the void acts like a converging lens. D. be bent away from the axis because the void acts like a converging lens. E. emerge parallel to the axis because the index of refraction of the lens is smaller than that of the surrounding plastic medium. 4. With a point source of light S a distance d in front of screen A, the intensity on the screen is I o. How is the light intensity I changed at the center of the screen if you put a mirror M a distance 3d behind the source? Approximate the light source as transparent. A S 3d d A. I/I o = 10/9 B. I/I o = 50/49 C. I/I o = 17/16 D. I/I o = 2 E. I/I o = 8/7 Page 2

3 5. The figure shows two rays of light encountering an interface, where they reflect and refract. Which of the resulting waves is shifted by a phase factor of π at the interface? A. a B. b C. c D. d E. none of the above 6. A scientist studying interference measures an on-axis intensity I 2 on a screen in a Young's two-slit interference experiment. When one of the slits is covered up, the intensity on the axis is A. I 2 B I 2 C I 2 D I 2 E I 2 7. Light of wavelength 500 nm impinges normally on a film of index 1.2 which is deposited on another very thick material of index 1.5. This wavelength exhibits a reflection maximum. What is the thickness of the thinnest film (with greater than zero thickness) compatible with this observation? A. 154 nm B. 208 nm C. 333 nm D. 413 nm E. 576 nm Page 3

4 8. Lenses are often given a thin coating of a transparent material to minimize unwanted reflections from the lenses, as shown. For this to be most effective, one needs: A. destructive interference between 1 and 2. B. constructive interference between 1 and 2. C. destructive interference between 3 and 4. D. constructive interference between 3 and 4. E. the speed of light in the coating to be less than that in the lens. 9. A laser beam of wavelength 600 nm is incident on two slits that are separated by 0.02 mm. What is the separation between adjacent bright maxima observed on a screen 5 m away? A. 0.1 mm B mm C. 1.1 mm D. 15 cm E. 20 mm 10. What is the change in phase experienced by a wave with frequency f = 3 x 10 9 Hz when it travels 10 cm through a medium with refractive index n = 2? A. π/2 rad B. π rad C. 2π rad D. 4π rad E. none of the above Page 4

5 11. A microwave interferometer using microwaves with wavelength of 3.0 cm is assembled from a microwave transmitter, a partially transmitting/partially reflecting surface, two reflecting surfaces, and a microwave receiver. With all the other elements in the apparatus fixed in position, by what distance does one of the reflecting surfaces have to move in order for the microwave receiver to register two adjacent maxima? A. 1.5 cm B. 3.0 cm C. 6.0 cm D cm E cm 12. The distance between the first and fifth minima of a single-slit diffraction pattern is 0.25 mm with the screen 50 cm away from the slit, using light of wavelength 469 nm. The slit width is: A. 1.0 mm B mm C mm D. 825 mm E mm 13. In the problem of single slit diffraction, phasors can be added up to represent contributions from different elements of the slit. If the phasors form a complete circle, this indicates that A. the net intensity is zero. B. the net intensity is a maximum. C. the intensity is one-half of the maximum. D. the phasor method is not a valid approximation. E. the position for which the intensity is being calculated is on the axis. 14. Suppose you are observing double slit diffraction with finite width slits, and for a certain monochromatic wavelength λ the number of double slit maxima within the central peak of the single slit interference pattern is 13. If you now double the wavelength, how many maxima occur in the central peak? A. 26 B. 25 C. 13 D. 7 E. 6 Page 5

6 15. The figure shows the bright fringes that lie within the central diffraction envelope in two double-slit diffraction experiments using the same wavelength of light. The figure is drawn to scale. Which of the following conclusions can you deduce from these patterns? A B A. The slit width a in experiment A is larger than that in experiment B. B. The slit separation d in experiment A is greater than that in experiment B. C. The ratio d/a in experiment A is greater than that in experiment B. D. The slit width a in experiment A is the same as that in experiment B. E. The slit separation d in experiment A is smaller than in experiment B. 16. In a double slit experiment, the spacing between the slits is mm and the width of each slit is 0.1 mm. How many interference fringes are observed within the central diffraction maximum? A. 17 B. 9 C. 15 D. 10 E. cannot be determined from the information provided 17. "Pointillist" paintings, such as those created by the artist Seurat, consist of many small closelyspaced dots of various colors arranged in a pattern on the canvas. As one changes one's viewing distance, the colors seen in the painting by the human eye (with pupil size of about 5mm) in a given region of the painting change because A. the dots, which must be roughly 0.2 mm apart, blend together by Raleigh's criterion B. the dots, which must be roughly 5mm apart, blend together by Raleigh's criterion C. the dots, which must be roughly 0.2mm apart, blend together by Fresnel diffraction D. the dots, which must be roughly 5mm apart, blend together by Fresnel diffraction E. the dots, which must be roughly 0.2mm apart, blend together due to dispersive effects in the human eye Page 6

7 18. Two identical radiators of waves, S1 and S2, are in phase and emit radiation at the same wavelength. They are separated by a distance d of 3 wavelengths. Find the shortest non-zero distance from S1, along the x-axis, for which maximally constructive interference occurs (see figure). Express this distance in units of wavelengths. A B C. 4.0 D. 3.0 E Unpolarized light is passed through two polarizing sheets and the plot shown of light intensity vs. angle between the polarizers is obtained. The data are fit to a function of the form I(θ) = a + bcos 2 θ. What was the intensity of the unpolarized light source? Assume the units in the plot are W/m 2. A. 1.0 W/m 2 B. 0.8 W/m 2 C. 0.6 W/m 2 D. 0.3 W/m 2 E. 0.1 W/m 2 Page 7

8 20. To obtain greater resolving power for a diffraction grating: A. the number of slits should be decreased. B. the slit width should be decreased. C. the slit width should be increased. D. the number of slits should be increased. E. the slit separation should be increased. Page 8

9 Answer Key for Test "214MidtermFa03.tst", 11/14/2003 No. in Q-Bank No. on Test Correct Answer C C B B D D B A D D A B A C C A A A C D Page 1